For a deck ledger board attached to a poured concrete or solid masonry wall, expansion anchors must use a 1/2 in. diameter bolt or threaded rod, stepping up to 5/8 in. diameter where fastener geometry demands it [S1][S2]. Embedment, spacing, and base-material choice drive the actual spec more than diameter alone.
This question is most often raised by residential builders attaching a 1-1/2 in. nominal ledger (2x lumber or 1 in. engineered wood product) across joist spans from 6 ft. to 18 ft., where fastener spacing must also track Table 6 values. Three base-material cases exist (solid concrete, solid masonry, hollow masonry) and each maps to a different anchor type, not just a different drill bit.
Code-Backed Diameter: 1/2 in. Rod, 5/8 in. When Geometry Forces It
The Wisconsin SPS 325 Appendix B and the model code carried on UpCodes both state the bolt or threaded rod of an expansion anchor must have a 1/2 in. diameter, with 5/8 in. diameter required in some cases [S1][S2]. That 5/8 in. caveat covers situations where the manufacturer-rated 1/2 in. expansion sleeve cannot deliver the required shear or tension capacity at the available embedment, so the designer steps the sleeve size up while keeping the rod diameter matched to the ledger hole pattern. Lead anchors are explicitly prohibited in the same code section [S2].
Through-bolts and adhesive anchors share the 1/2 in. minimum, with through-bolts requiring 17/32 in. to 9/16 in. pilot holes [S2]. Washers are mandatory at both the bolt head and the nut for through-bolts, and at the bearing face for expansion anchors, because the ledger-side crushing load under cyclic deck movement is what progressively splits untreated ledger stock.
Embedment by Base Material: 2-1/2 in. to 4-1/4 in. Minimums
Solid masonry requires expansion anchors set at least 2-1/2 in. into the wall, per the Decks.com reference for ledger-to-solid-masonry attachment [S5]. Solid poured concrete is the case where specs push harder: a June 2026 BuildToolHQ guide specifies 1/2 in. wedge anchors with at least 3.5 in. embedment into the concrete, with a 4 in. embedment called out by an Ontario designer in a DIY forum thread for the same 1/2 in. wedge anchor [S3][S4].
Hollow masonry forces a different anchor system entirely. Approved adhesive anchors with a 1/2 in. threaded rod (examples named in code: Epcon Acrylic 7 by ITW Ramset/Red Head, and HY-20 by Hilti) are required, and Decks.com sets the epoxy depth at a minimum 4-1/4 in. into the wall [S1][S2][S5]. The adhesive cartridge must be left on site for inspector verification, which is a procedural tell that the connection is treated as a critical, design-bearing element rather than a commodity fastener.
Anchor Type Comparison for Ledger-to-Concrete
Three anchor families cover the practical cases; the right one is set by base material, not by price. Wedge anchors are the default for solid poured concrete walls, sleeve anchors are the fit for concrete block (CMU) face shells, and epoxy or adhesive anchors handle hollow block and cracked concrete [S3].
The June 2026 BuildToolHQ table lines them up on three decision criteria: a 1/2 in. x 5-1/2 in. wedge anchor rates roughly 4,000 lb shear in solid concrete, a 1/2 in. x 5 in. sleeve anchor roughly 2,500 lb shear in CMU, and a 1/2 in. epoxy-anchored threaded rod roughly 6,000+ lb shear, with epoxy being the only one of the three that works in a hollow cell because the adhesive fills the void [S3]. Wedge anchors placed in hollow CMU have nothing to expand against, which is the single most common failure mode at this connection after flashing omissions.
Spaced at 16 in. on center maximum and staggered in two rows, a 1/2 in. wedge anchor is the residential default for solid concrete [S3]. Stacked-washer through-bolts with 1/2 in. washers can extend spacing to 36 in. on center for 2x lumber at short joist spans, per Table 6, but the 1/2 in. maximum gap between the ledger face and the wall sheathing, and the 1 in. maximum stand-off when sheathing is present, still apply [S2].
Selection Criteria: Base Material, Spacing, and Flashing
The first decision is base material, because it dictates anchor family. Solid poured concrete points to a 1/2 in. wedge anchor at 3.5 in. to 4 in. embedment, solid brick or solid concrete masonry to a 1/2 in. expansion anchor at 2-1/2 in. minimum embedment, and hollow CMU to either grout-filled cells with expansion anchors or 1/2 in. threaded rod on approved epoxy at 4-1/4 in. depth [S1][S2][S3][S5].
Second is spacing, governed by joist span and band-board material per Table 6: for 2x lumber band joists, lag screws and through-bolts step from 30 in. on center at 6 ft. spans down to 10 in. on center at 18 ft. spans, while adhesive anchors hold a flatter 32 in. to 16 in. on center across the same range [S2]. Bolts should be staggered between joists and kept 2 in. from the top and bottom edges of the ledger to avoid splitting [S5].
Third is the corrosion chain, which matters as much as the anchor spec: ACQ-treated ledger stock demands hot-dipped galvanized or stainless steel anchors and washers, since standard zinc-plated steel corrodes rapidly inside ACQ [S3]. Flashing must be installed before any anchor is set, because water infiltration at the ledger-to-concrete interface is what destroys the wood the anchor is bearing against. For related spec-side detail on how embedded metals and base materials interact in service, see EPS board selection in insulated assemblies and the broader insulation board reference, which cover moisture-managed assemblies relevant to ledger flashing terminations.
Who This Spec Is For, and Where It Breaks Down
This anchor spec is for residential and light-commercial decks with a single-story ledger-to-poured-concrete or ledger-to-solid-masonry connection, using 2x or EWP ledgers across spans up to 18 ft. It also covers retrofit deck builds where a free-standing deck is not feasible due to footing constraints. Builders working to a designer spec calling out 1/2 in. at 4 in. embedment on solid concrete should order 1/2 in. x 7-1/8 in. carbon or galvanized wedge anchors (Power Stud cat. 7427 is a real catalog match for that combination) rather than a 5-1/2 in. anchor, which only delivers about 3-1/2 in. of usable embedment once the nut, washer, and thread engagement are accounted for [S4].
The spec does not apply to cracked concrete without epoxy, to hollow CMU without either grout-fill or adhesive, to ledgers carrying roof loads, or to multi-story assemblies that fall under engineered-design rules outside the prescriptive table. Anyone with spalled, crumbly, or otherwise deteriorated concrete should stop and call a structural engineer; expansion anchors in degraded base material have no reliable capacity [S3].
Installation Discipline and Verifiable Next Steps
Two installation facts are non-negotiable in code. First, expansion anchors must be installed per the manufacturer's instructions, equipped with washers, and for adhesive anchors the cartridge must remain on site for the inspector [S1][S2]. Second, through-bolts should be re-tightened 6 to 12 months after construction to compensate for wood shrinkage, a step the same code section calls out explicitly [S2].
Track these signals on the next ledger build: (1) the building department's published fastener schedule, which will be either the prescriptive Table 6 spacing or an engineered alternate stamped to ACI 318, and (2) the anchor cartridge label left on site, which has to match the approved adhesive system list in the local adoption of the IRC. For adjacent spec reading on how ledger loads feed into broader structural assemblies, the XPS board continuous-insulation reference and the structural expansion joint page are useful companions when detailing the deck-to-house interface against the foundation wall.
Background reading: Aluminum Die Casting Die Temperature Control for Dimensional Stability.